This invention pertains to transmissions, and more particularly to an improved gear shifting arrangement for an in-line transmission, and a ring gear assembly for a differential.
One of the objectives of the present invention is to improve upon the shifting operation of the transmission disclosed in U.S. Pat. No. 3,812,735 issued on May 28, 1974, and assigned to the assignee of the present invention. In that particular transmission, a plurality of gears are freely journalled on one end of an intermediate shaft and a reverse gear is mounted on the opposite end of the intermediate shaft. Gear selection is accomplished by a key slidably disposed in a groove axially disposed in the outer surface of the intermediate shaft, wherein one end of the key is yieldably biased radially outwardly from the outer surface of the intermediate shaft. A shifting mechanism selectively slides the key within the groove so that the forward gears may be individually selected with the biased end of the key and reverse gear may be selected by the opposite, blunt end of the key. Because the end of the key which engages the forward gears is biased radially outwardly, engagement of a selected gear is always possible since the biased end of the key may be moved radially inwardly by each gear to engage a particular key-engaging slot in the gear bore, regardless of the angular position of the gear on the shaft relative to the key. However, since reverse gear is selected by the opposite, blunt end of the key, which blunt end is not biased radially outwardly, engagement of reverse gear upon sliding the key within the groove is not always assured, and in those instances where the blunt end of the key does not initially engage the key-engaging slot in the bore of the reverse gear, double-clutching is required to properly engage the blunt end with the key-engaging slot. Such double-clutching is undesirable and time-consuming, and in certain circumstances may be cumbersome or difficult to perform.
In those transmissions and transaxles utilizing differentials, disadvantages exist in the assembly of the ring gear and bevel gear arrangement. Specifically, some transmissions and transaxles utilize a differential carrier of single-piece, cast iron construction to carry side-by-side the ring gear and bevel gears. Because this differential carrier must support both the ring gear and bevel gears separately, it is generally a heavy, large item requiring a large number of support bearings, or fewer support bearings having stronger material properties to satisfactorily support the differential carrier within the transmission or transaxle.
This particular differential carrier therefore adds undesirable costs to the product in terms of parts and labor.
A prior art transmission in which the carrier is eliminated is disclosed in U.S. Pat. No. 4,232,569 issued on Nov. 11, 1980. In this particular transaxle, the differential carrier is eliminated and the ring gear carries the bevel gears within its interior by means of a supporting center pin. This particular transaxle has consequently disposed with the differential carrier and the additional bearing requirements thereof. However, by eliminating the support bearings necessary for a differential carrier, other bearing support is required and is provided by this particular transaxle by a pair of annular shoulders on the ring gear and a complementary pair of annular shoulders in the housing cavity containing the differential. As disclosed in this particular patent, the annular shoulders of the cavities form the full bearing surfaces for the ring gear annular shoulders, and also serve to keep the teeth of the ring gear radially spaced apart from the inner surface of the housing cavity.
The bearing surfaces provided by the annular shoulders of the housing cavity are not particularly large and it is generally well known that the smaller the bearing surface area for a given exerted force, the greater the pressure loads experienced by that smaller bearing surface. Disadvantages generally resulting from smaller bearing surfaces are higher running temperatures within the housing and a generally shorter useful life.
Another costly disadvantage with some of the prior art transmissions and transaxles is present when a single-piece input shaft is used to transfer power to the intermediate shaft and thereafter to the output shafts. Such single-piece input shafts generally extend the full length of the housing and the forces exerted thereon may cause the input shaft to tend to bow or twist. Eventually, these exerted forces against the input shaft cause premature failure of the bearings supporting the input shaft within the housing, thereby requiring disassembly of the transmission or transaxle, replacement of the prematurely failed bearings, and reassembly thereof at an undesirable cost in material and labor.